Power saving wireless local area network portable device

ABSTRACT

A system and method are provided for controlling bandwidth allocation in a wireless local area network (wLAN). The method comprises: expressing device bandwidth allocations in terms of a time base; in response to expressing the bandwidth allocation in terms of a time base, monitoring network communications; and, measuring the allocated bandwidths. The method may further comprise: establishing polling schedules in response to expressing the bandwidth allocation in terms of a time base; and, de-energizing devices in response to the polling schedules. Expressing device bandwidth allocations in terms of a time base includes establishing: an inter-transmission opportunity (TXOP) interval; and, a TXOP jitter. These fields are supplied in the IEEE 802.11e transmit specification (TSPEC). Then, de-energizing devices in response to the polling schedule includes disengaging transmission and receiving functions in the minimum TXOP intervals between polling events, where the minimum TXOP interval is the inter-TXOP interval minus the TXOP jitter.

RELATED APPLICATIONS

This application is a Divisional Application entitled, SYSTEM AND METHODFOR CONTROLLING WIRELESS LAN BANDWIDTH ALLOCATION, invented by Kandalaet al., Ser. No. 10/497,573, filed Jun. 1, 2004, U.S. Pat. No.7,414,986;

which claims the benefit of a provisional application entitled, METHODSAND SYSTEMS FOR ALTERNATIVE TRAFFIC SPECIFICATION PARAMETERS, inventedby Ohtani et al., Ser. No. 60/400,511, filed Aug. 2, 2002. Both theabove-mentioned applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to IEEE 802.11 communications and, moreparticularly to a system and method for establishing a time-basedbandwidth allocation protocol that, in turn, permits bandwidthmonitoring and battery-operated devices to implement power saving cyclesbetween transmissions.

2. Description of the Related Art

As noted in “A Short Tutorial on Wireless LANs and IEEE 802.11 by Lough,Blankenship and Krizman(computer.org/students/looking/summer97/ieee802), the IEEE 802.11standard places specifications on the parameters of both the physical(PHY) and medium access control (MAC) layers of the network. The PHYlayer, which actually handles the transmission of data between nodes,can use either direct sequence spread spectrum, frequency-hopping spreadspectrum, or infrared (IR) pulse position nodulation. IEEE 802.11 makesprovisions for data rates from 1 Mbps to 54 Mbps, and calls foroperation in the 2.4-2.4835 GHz frequency band (in the case ofspread-spectrum transmission), which is an unlicensed band forindustrial, scientific, and medical (ISM) applications. IEEE 802.11 alsomakes provision for data rates from 6 Mbps to 54 Mbps, and calls foroperation in the 5.2 and 5.8 U-NII (Unlicensed InformationInfrastructure) band.

The MAC layer is a set of protocols that is responsible for maintainingorder in the use of a shared medium. The 802.11 standard specifies acarrier sense multiple access with collision avoidance (CSMA/CA)protocol. In this protocol, when a node receives a packet to betransmitted, it first listens to ensure no other node is transmitting.If the channel is clear, it then transmits the packet. Otherwise, itchooses a random “backoff factor” which determines the amount of timethe node must wait until it is allowed to transmit its packet. Duringperiods in which the channel is clear, the transmitting node decrementsits backoff counter. When the channel is busy it does not decrement itsbackoff counter. When the backoff counter reaches zero, the nodetransmits the packet. Since the probability that two nodes will choosethe same backoff factor is small, collisions between packets areminimized. Collision detection, as is employed in Ethernet, cannot beused for the radio frequency transmissions of IEEE 802.11. The reasonfor this is that when a node is transmitting it cannot hear any othernode in the system which may be transmitting, since its own signal willdrown out any others arriving at the node.

Whenever a packet is to be transmitted, the transmitting node firstsends out a short ready-to-send (RTS) packet containing information onthe length of the packet. If the receiving node hears the RTS, itresponds with a short clear-to-send (CTS) packet. After this exchange,the transmitting node sends its packet. When the packet is receivedsuccessfully, as determined by a cyclic redundancy check (CRC), thereceiving node transmits an acknowledgment (ACK) packet. Thisback-and-forth exchange is necessary to avoid the “hidden node” problem.In the hidden-node situation node A can communicate with node B, andnode B can communicate with node C, however, node A cannot communicatenode C. Thus, for instance, although node A may sense the channel to beclear, node C may in fact be transmitting to node B. The protocoldescribed above alerts node A that node B is busy, and hence it mustwait before transmitting its packet.

Local area networks (LANs) typically use a Carrier Sense Multiple Access(CSMA) scheme, in order to support parameterized Quality of Service(QoS). To support packet transmission meeting requirements forthroughput, latency and jitter, the system must be able to allocate timeon the channel in such a way that coexistence with CSMA-basedtransmissions is not greatly affected. Moreover, packet error rates insuch systems are typically large if the medium is wireless or power-linebased, typically greater than 10%.

Several solutions have been proposed to solve the problem of packettransport meeting parameterized QoS objectives. However, these proposalshave been found lacking in one or more aspects. The original drafts of802.11e included an object called a TSPEC (for TransmissionSpecification), but no means were provided for specifying an upper boundon channel occupancy required for admission in a given stream. Nor wasany means provided for objectively verifying that a request for thetransport of packets meeting specific QoS objectives could be met.

In addition, this type of TSPEC is agnostic to the fact that the channelmakes errors, and therefore, an over-reservation of bandwidth isgenerally required. Moreover, this type of TSPEC could not be used withpower saving devices, since there was no guarantee of time when asequence of packets wouldn't be delivered.

Time-based polling techniques have previously been considered. However,no time-based polling techniques have been suggested that guarantee atime when polling does not occur. Moreover, previous time-based pollingtechniques have failed to considered hybrid coordinator (HC) or accesspoint (AP) negotiation; that the HC/AP must act as coordinator forallocation of time on the channel. Finally, no time-based pollingtechniques have considered a method for making bandwidth reservations.

It would be advantageous if a time-based polling method could beestablished between IEEE 802.11e network devices to measure allocatedbandwidth.

It would be advantageous if a time-based bandwidth allocation protocolcould be established between IEEE 802.11e devices so that batterypowered portable units could be de-energized in predictable intervalsbetween communications.

SUMMARY OF THE INVENTION

The present invention simplifies the parameterized QoS transportmechanism of 802.11e communications. The present invention incorporatesa reservation mechanism that permits an AP to manage bandwidth, locally.More specifically, a hybrid coordinator (HC), collocated with the AP,provides the polling and scheduling services needed to manage thebandwidth. The format permits polling sequences to be predictablydetermined, allowing for power savings in the intervals when the devicesare not transmitting or receiving polls.

The present invention provides a method for objectively determiningscheduled opportunities for transmission (TXOPs) with parameterized QoSpacket transport based on channel conditions, and for reporting that toan HC/AP. Further, a method is provided for observing said TXOPs, toverify the interoperability of different vendors' implementations.Finally, the present invention method provides parameterized QoSservices that coexist with prioritized quality of service CSMA basedtraffic, and enable priority differentiation to be maintained, subjectto limits on admitted parameterized QoS traffic.

Accordingly, a method is provided for controlling bandwidth allocationin a wireless local area network (wLAN), for example, in an IEEE 802.11enetwork. The method comprises: expressing device bandwidth allocationsin terms of a time base; in response to expressing the bandwidthallocation in terms of a time base, monitoring network communications;and, measuring the allocated bandwidths. Other aspects of the methodfurther comprise: establishing polling schedules in response toexpressing the bandwidth allocation in terms of a time base; and,de-energizing devices in response to the polling schedules.

Expressing device bandwidth allocations in terms of a time base includesestablishing: an inter-transmission opportunity (TXOP) interval; and, aTXOP jitter. These fields are supplied in the transmit specification(TSPEC) sent in the QoS negotiation process. Then, de-energizing devicesin response to the polling schedule includes disengaging transmissionand receiving functions in the minimum TXOP intervals between pollingevents. The minimum TXOP interval is defined as the inter-TXOP intervalminus the TXOP jitter.

Additional details of the above-described method and a wLAN system forcontrolling bandwidth allocation are provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the present invention wirelesslocal area network (wLAN) system for controlling bandwidth allocation.

FIG. 2 is a timing diagram depicting time-based events associated withthe first STA.

FIG. 3 is a diagram depicting a TSPEC format supportive of the presentinvention system.

FIG. 4 is a diagram depicting the sequence of messages used in a TRSetup, to request a QoS.

FIG. 5 is a flowchart illustrating the present invention method forcontrolling bandwidth allocation in a wireless local area network(wLAN).

FIG. 6 is a flowchart illustrating the present invention method forsaving portable device power in a wireless local area network (wLAN).

FIG. 7 is a flowchart illustrating another aspect of the presentinvention method for saving portable device power in a wLAN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic block diagram of the present invention wirelesslocal area network (wLAN) system for controlling bandwidth allocation.The system 100 comprises at least one QoS station (QSTA), referred toherein as a station (STA). Shown are two STAs, a first STA 102 and asecond STA 104, however, the system is not limited to any particularnumber of STAs. Each STA, as exemplified by first STA 102, has awireless port 106 to communicate information in a bandwidth allocationexpressed in terms of a time base. The wireless communication link isrepresented by reference designator 108. A hybrid coordinator 110 (HC),associated with the second STA 104, has a wireless communications port112 to monitor the first STA 102 communications and measure theallocated STA bandwidths. The HC may also monitor the second STA 104transmissions, or other STAs (not shown) that are in communication witheither the first STA 102 or the second STA 104.

The HC 110 establishes and transmits polling schedules to the first STA102, or other STAs (not shown) communicating with the HC 110, responsiveto the time-based bandwidth allocation. The first STA 102 de-energizesdevices in response to the received polling schedules. Morespecifically, the first STA 102 communicates in a bandwidth allocationexpressed in terms of a time base having an inter-transmissionopportunity (TXOP) interval and a TXOP jitter. That is, the time-basedpolling schedules permit the first STA 102 to determine an inter-TXOPinterval and TXOP jitter between scheduled communications.

FIG. 2 is a timing diagram depicting time-based events associated withthe first STA. Shown is the inter-TXOP interval, or mean TXOP intervalbetween communications, and TXOP jitter, or mean TXOP variance. Thefirst STA communicates in a time base having an inter-TXOP interval anda TXOP jitter, in response to receiving a transmit specification (TSPEC)with inter-TXOP and TXOP jitter fields.

FIG. 3 is a diagram depicting a TSPEC format supportive of the presentinvention system. Shown are inter-TXOP and TXOP jitter fields.Conventionally, minimum data rate, mean data rate, and maximum burstsize fields have been suggested for use in defining the allocated datarate, the TXOP duration, and the latency. However, to support atime-based bandwidth allocation method, the TSPEC element of FIG. 3shows a minimum TXOP duration field, which replaces the minimum datarate field, a nominal TXOP duration field to replace the mean data ratefield, and a maximum TXOP duration field to replace maximum burst sizefield. The use of time-based fields permits an entity, such as the HC,to actually measure the allocated data rate using the TXOP durationfields. The TXOP interval fields permit the interval between TXOPdurations to be predictive, to support power saving functions.

FIG. 4 is a diagram depicting the sequence of messages used in a TRSetup, to request a QoS. Viewing both FIGS. 1 and 4, the first STA 102requests permission to communicate traffic information at a secondbandwidth. The second bandwidth is defined as a desired first bandwidthplus a surplus bandwidth allowance. In other words, a QoS is requested.A first STA station management entity (SME) 150 sends aMLME-ADDTS.request to the first STA MAC 152. The request includes theabove-mentioned TSPEC. The first STA MAC 152 generates a frame tosupport PHY level communications and sends the request to the HC MAC 110associated with the second STA 104. The HC MAC 110 relays the requestfrom the first STA to the second station SME, sending aMLME-ADDTS.indication primitive to a second STA SME 154. The second STASME 154 processes the request and transmits a response to the first STAvia the HC 110, including an allocation to communicate with the secondSTA at the second bandwidth. This allocation is more an acknowledgementof the TSPEC request from the first STA. More specifically, the secondSTA SME 154 generates a MLME-ADDTS.response. The HC MAC 110 generatesthe proper frame for communications with the first STA MAC 152, and thefirst STA MAC 152 sends a MLME-ADDTS.confirm primitive to the first STASME 150. Once the TSPEC has been confirmed, the second STA SME 154 caninitiate polling events.

Returning to FIG. 2, once the TR Setup is established, the first STAtransmits traffic information to the second STA at the second bandwidth.That is, the first STA can downlink transmissions to the second STA, orother stations, in the TXOP duration derived with respect to the pollingevent. Alternately stated, the HC, in response to establishing a pollingschedule, sends a poll to the first STA and the first STA transmits inthe TXOP durations derived from the TSPEC. Typically, there is a shortinter-frame spacing (SIFS) between the poll and the TXOP duration thatis not shown in the figure.

The HC monitors first STA traffic channel TXOP durations, the PHY datarate within the TXOPs, and the intervals between TXOPs, and measures theallocated bandwidth by calculating the ratio of transmitted bits (TXOPduration×PHY data rate) to TXOP intervals. The first STA de-energizes inthe TXOP intervals between polling events, and saves power in responseto de-energizing. More specifically, the first STA disengagestransmission and receiver functions in the minimum TXOP intervals, wherethe minimum TXOP interval is equal to the inter-TXOP interval minus theTXOP jitter.

Functional Description

In the IEEE 802.11e standard, Quality of Service enhancements are beingmade that allow for prioritized Quality of Service; i.e., a service thatallows connectionless packet data services to be sent at differingpriorities. This service permits some packets to be transmitted beforeother, lower priority, packets, irrespective of when they arrive at thetransmitting client. In addition, provisions are being made in thestandard to allow a polling service to enable the transmission ofparameterized QoS traffic. That is, traffic that must be transmittedsubject to constraints on throughput, latency and jitter.

In order to provide both services the following requirements must bemet:

1. The parameterized Quality of Service must provide for the fact thatthe channel is error prone.

2. The parameterized QoS must be observable, and testable, so thatscheduled allocations of transmission on the channel (“TXOPs”) can bemeasured and so that equipment can be certified to be interoperable.

3. There must be an admission control mechanism to limit the occupancyof parameterized QoS transport on the channel to maintain prioritizedQoS traffic.

4. There must, in scheduling prioritized QoS traffic, be allocatedperiods of time when transmissions do not happen, so that mobile devicescan conserve battery power.

FIG. 5 is a flowchart illustrating the present invention method forcontrolling bandwidth allocation in a wireless local area network(wLAN). Although the method is depicted as a sequence of numbered stepsfor clarity, no order should be inferred from the numbering unlessexplicitly stated. It should be understood that some of these steps maybe skipped, performed in parallel, or performed without the requirementof maintaining a strict order of sequence. The method starts at Step500.

Step 502 expresses device bandwidth (BW) allocations in terms of a timebase. Step 504, in response to expressing the bandwidth allocation interms of a time base, establishes polling schedules. Step 506, inresponse to expressing the bandwidth allocation in terms of a time base,monitors network communications. Step 508 measures the allocatedbandwidths. Step 510 de-energizes devices in response to the pollingschedules.

In some aspects of the method, expressing device bandwidth allocationsin terms of a time base in Step 502 includes substeps. Step 502 aestablishes an inter-transmission opportunity (TXOP) interval. Step 502b establishes a TXOP jitter. Establishing an inter-TXOP interval (Step502 a) and a TXOP jitter (Step 502 b) includes establishing (est.) atransmit specification (TSPEC) communication with inter-TXOP intervaland a TXOP jitter fields.

In other aspects, expressing device bandwidth allocations in terms of atime base in Step 502 includes additional substeps where a TSPECcommunication establishes a minimum TXOP duration field in Step 502 c, anominal TXOP duration field in Step 502 d, and a maximum TXOP durationfield in Step 502 e.

In other aspects the method, expressing device bandwidth allocations interms of a time base (Step 502) includes additional substeps. In Step502 f, a first station (STA) requests permission to communicate trafficinformation at a second bandwidth, with a second STA. The secondbandwidth is defined as the first (desired) bandwidth plus a surplusbandwidth allowance. As noted above in the explanation of the system,the request is in the form of a TSPEC as defined in Steps 502 a through502 e. In Step 502 g a hybrid controller (HC) relays the request to thesecond STA. In Step 502 h the second STA transmits a response, whichincludes an allocation to the first STA allocation to communicate withthe second STA at the second bandwidth. In Step 502 i, the HC relays theresponse to the first STA. Then, in Step 505, the first STA transmitstraffic information to the second STA through a wireless medium at thesecond bandwidth.

In other aspects, establishing polling schedules in response toexpressing the bandwidth allocation in terms of a time base in Step 504includes substeps. In Step 504 a the HC establishes a polling schedule.In Step 504 b the HC sends a poll to the first STA in response to thepolling schedule. Then, the first STA transmitting traffic informationto the second STA through a wireless medium at the second bandwidth(Step 505) includes the first STA transmitting in the TXOP durationsderived from the TSPEC.

In some aspects, monitoring network communications in response toexpressing the bandwidth allocation in terms of a time base (Step 506)includes the HC monitoring first STA traffic channel TXOP durations, thePHY data rate within the TXOPs, and the intervals between TXOPs. Then,measuring the allocated bandwidths in Step 508 includes the HCcalculating the ratio of transmitted bits (TXOP duration×PHY data rate)to TXOP intervals for the first STA.

In other aspects, de-energizing devices in response to the pollingschedule in Step 510 includes de-energizing devices in the TXOPintervals between polling events. Then, the method comprises a furtherstep. Step 512 saves device power in response to de-energizing thedevices.

In some aspects, de-energizing the devices in the TXOP intervals betweenpolling events (Step 510) includes the first STA disengagingtransmission and receiving functions in the minimum TXOP intervals,where the minimum TXOP interval is equal to the inter-TXOP intervalminus the TXOP jitter.

FIG. 6 is a flowchart illustrating the present invention method forsaving portable device power in a wireless local area network (wLAN).The method starts at Step 600. Step 602 expresses device bandwidthallocations in terms of a time base. Step 604, in response to expressingthe bandwidth allocation in terms of a time base, establishes pollingschedules. Step 606 de-energizes devices in response to the pollingschedules.

FIG. 7 is a flowchart illustrating another aspect of the presentinvention method for saving portable device power in a wLAN. The methodstarts at Step 700. Step 702 expresses device bandwidth allocations interms of a time base. Step 704, in response to expressing the bandwidthallocation in terms of a time base, establishes polling schedules. Step706 polls the STAs in response to the polling schedules. Step 708, inresponse to expressing the bandwidth allocation in terms of a time base,establishes station (STA) transmission schedules. That is, the STAtransmission schedules are established in response to the polling. TheTXOP durations can be derived from the TSPEC fields (Step 702) and thepolling events (Step 706). Step 710 de-energizes STAs in response to thetransmission schedules.

A system and method have been presented for controlling bandwidthallocations and saving power in a wLAN using a time-based TSPEC fields.Some examples have been used to illustrate concepts, however, thepresent invention is not limited to merely these examples. Although thepresent invention has been described in the context of a 802.11 wirelessLAN system, it is equally applicable to any other CSMA based system, inparticular, power line communications. Other variations and embodimentsof the invention will occur to those skilled in the art.

1. In a wireless local area network (wLAN), a method for saving portabledevice power, the method comprising: expressing device bandwidthallocations in terms of a time base by establishing: aninter-transmission opportunity (TXOP) interval; and, a TXOP jitter; inresponse to expressing the bandwidth allocation in terms of a time base,establishing station (STA) transmission schedules; and, de-energizingSTAs in response to the transmission schedules.
 2. The method of claim 1further comprising: in response to expressing the bandwidth allocationin terms of a time base, establishing polling schedules; polling theSTAs in response to the polling schedules; and, wherein establishingstation (STA) transmission schedules includes establishing transmissionschedules in response to the polling.
 3. The method of claim 1 whereinestablishing an inter-TXOP interval and a TXOP jitter includesestablishing a transmit specification (TSPEC) communication withinter-TXOP interval and a TXOP jitter fields.
 4. The method of claim 3wherein expressing device bandwidth allocations in terms of a time baseincludes establishing a TSPEC communication with fields including: aminimum TXOP duration; a nominal TXOP duration; and; a maximum TXOPduration.
 5. The method of claim 4 wherein expressing device bandwidthallocations in terms of a time base includes: a first station (STA)requesting permission to communicate traffic information at a secondbandwidth, with a second STA, where the second bandwidth is defined as afirst desired bandwidth plus a surplus bandwidth allowance; a hybridcontroller (HC) relaying the request to the second STA; the second STAtransmitting a response, including a first STA allocation to communicatewith the second STA at the second bandwidth; the HC relaying theresponse to the first STA; and, the method further comprising: the firstSTA transmitting traffic information to the second STA through awireless medium at the second bandwidth.
 6. In a wireless local areanetwork (wLAN), a system for saving portable device power, the systemcomprising: at least one station (STA), each STA having a wireless portto communicate information in a bandwidth allocation expressed in termsof a time based transmission schedule having an inter-transmissionopportunity (TXOP) interval and a TXOP jitter, and de-energize inresponse to the transmission schedule.
 7. The system of claim 6 furthercomprising: a hybrid coordinator (HC) having a wireless communicationsport to monitor the STA communications and measure the allocated STAbandwidths, establish polling schedules, and poll the STAs in responseto the polling schedules; and, wherein each STA de-energizes in responseto polling by the HC.
 8. The system of claim 6 wherein the STAcommunicates in a time base having an inter-TXOP interval a TXOP jitter,in response to receiving a transmit specification (TSPEC) communicationwith inter-TXOP and TXOP jitter fields.
 9. The system of claim 8 whereinthe STA receives a TSPEC communication with a minimum TXOP durationfield, a nominal TXOP duration field, and a maximum TXOP duration field.10. The system of claim 9 further comprising: a first station (STA) witha wireless communications port requesting permission to communicatetraffic information at a second bandwidth, where the second bandwidth isdefined as a first desired bandwidth plus a surplus bandwidth allowance;wherein the HC includes a second STA with a station management entity(SME), the HC relaying the request from the first STA to the secondstation SME, the second STA SME transmitting a response to the first STAvia the HC, including an allocation to communicate with the second STAat the second bandwidth; and, wherein the first STA transmits trafficinformation to the second STA at the second bandwidth.
 11. The system ofclaim 10 wherein the HC, in response to establishing a polling schedule,sends a poll to the first STA; and, wherein the first STA transmits inthe TXOP durations derived from the TSPEC.